A need has existed for a low-cost computer output recording apparatus and method which has a character writing speed of approximately 4,000 characters per second upwards to 1,000,000 characters per second and more, particularly for a speed of approximately 40,000 characters per second which is suited to the state of the art apparatus. The apparatus and method should be capable of use with a relatively insensitive dry-processed photographic recording medium such as, for example, microfilm. The laser scanner of the present invention fulfills this need in a novel and simple manner.
To better understand the invention, brief reference is made to several prior art systems. Typical of the prior art devices is U.S. Pat. No. 3,324,478 to Jacobs and entitled, "Oscillographic Recording with Coherent Light". The Jacobs device utilizes an acoustooptic cell to deflect a coherent beam of light by Bragg reflection in accordance with the value of an input signal to the cell. Thus, an oscillographic recording can be made. However, only one frequency can be induced within the acoustooptic cell at any point in time in this device. Therefore, the cell emits only one diffracted beam of light which continuously varies in amount of deflection in accordance with the variation in frequency induced in the cell. It is readily apparent that only one scanning beam at a time can be provided by this device and that no provision is made to induce a plurality of separate and distinct frequencies simultaneously on the cell to produce a plurality of simultaneous light beam outputs. Furthermore, it is clear that this device is not adapted or designed to provide an output from a storage medium but is rather merely a convenient means for recording the deflection of a galvonometer coil.
Another prior art device is that disclosed by U.S. Pat. No. 3,397,605 to Brueggemann and entitled, "Frequency Modulated Radiant Energy Scanner Employing Cavitation-Induced Diffraction". This device, as the title indicates, relies upon cavitation forming bubbles in a liquid cell as a diffractor. One frequency at a time is used since varying bubble spacing is what variably diffracts the input beam. The cavitation effect is an entirely different phenomenon from that utilized by the present invention. The cavitation cell requires a higher energy input to a liquid cell than does the acoustooptic cell of the present invention. It is also evident that a solid cell cannot be utilized by the Brueggemann device. In addition, scanning, as in many other prior art devices, is accomplished with changing the diffraction angle by varying the frequency applied to the cell rather than by the inexpensive and efficient mechanical scanning means used in accordance with the present invention. In fact, this type prior art device is not adaptable for use with mechanical scanning means since the cell itself accomplishes the scanning with a variable single frequency control and this limits the scan to a single beam.
Yet another prior art device is that disclosed in U.S. Pat. No. 3,531,184 to Robert Adler entitled, "Acoustical Light Signal-Translating Apparatus". This device scans by using successive Bragg reflections of one light beam passed through two acoustooptic cells. Variable frequencies are imposed on the acoustooptic cells through which the light beam is passed to effect a raster type scan. By reason of the change in frequencies, the single diffracted beam scans in two directions within a plane. The raster scanning motion is achieved by incrementally changing the amount of diffraction in one cell and by synchronizing this change with the cycle of the other variable frequency such that two dimensional raster type scanning, such as achieved in a cathode ray tube results. Again, in this prior art device, as in the above mentioned prior art devices there is only one diffracted beam output at any time. In order to achieve the two dimensional region of scan, two separate acoustooptic cells, frequency generators and transducers are required. The resulting output is very similar to the recording oscillograph of Jacobs in that only one output beam at a time records a path on a recording medium or other receiving means. There is no disclosure of a way to simultaneously generate a plurality of output beams to achieve character writing with a single scan of a plurality of beams as with the present invention and it is very clear that no such use is achievable with, or contemplated by, the Adler device.
In accordance with the invention, a light source, for example, a helium neon gas or other type of laser is used to pass a light beam through an acoustooptic cell, which is preferably of water, although other materials including solids suffice, and which is used as a modulator and character height deflector. Unmodulated light transmitted through the modulator is blocked by a mask or other equivalent deflecting means. A scanner directs the modulated beams to a receiving medium. The scanner is preferably a rotating prism, but can also be a single flat mirror, mirror wheel or other rotating reflective device. Receiving medium motion can alternatively be used to fully or partially provide relative beam-to-recording medium motion. Relatively simple electronic circuitry, some of which is readily available and the rest of which can easily be fabricated onto a circuit card, is used for controlling the acoustooptic cell and scanner. In addition, low-precision, low-cost mechanical components are sufficient for use with this device.
As used herein, the terms light, optical and sound or acoustic are most general. That is, light or optical embraces ordinary visible light waves as well as electromagnetic wave energy at wavelengths above and below the visible portion of the spectrum. The term acoustic, as well as sound, refers to propagated wave energy and includes not only that in the audible range, but also wave energy up to and including, for example, the microwave frequencies which includes the ultrasonic frequencies of the preferred embodiment.
One object of this invention is to provide an apparatus and method for high-speed recording of stored information onto a photosensitive or other recording medium.
Another object of this invention is to provide a plural beam information recording system wherein every beam is discretely positioned and modulated.
Yet another object of this invention is to produce a printout record of one line of character information per scan on a photostorage medium which can be moving.
It is still another object of this invention to provide a method of, and apparatus for, high-speed recording of characters and other forms of information, such as graphic, picture, charts and drawings from computer storage.
It is yet another object of this invention to provide an information display system wherein a simultaneous plurality of light elements provide the readout.
One advantage of the present invention is that an array of light elements corresponding to character height is generated simultaneously rather than one at a time as in prior art systems to thus provide an increase in information recording rate with a corresponding decrease in energy density per light element.
Another advantage of the invention is that the recording can be of one complete line of characters at a time across an area of recording medium at very high speed.
Another advantage of the invention is that relatively inexpensive mechanical scanning components can be used in practicing the invention, thereby reducing the cost and complexity of a recording device.
Yet another advantage of the invention is that relatively insensitive dry-processed microfilm can be used as a recording medium.